Researchers work to make spray application more cost-effective, sustainable for apple growers

Rows of apple trees. Tractor-pulled airblast sprayer traveling between the rows of trees.
An intelligent spraying system mounted on an airblast sprayer can detect where apple trees’ foliage is located and activate spray nozzles to specifically target the foliage. Iowa State researchers are part of a team studying how low spray rates can go with this system, while still maintaining adequate application coverage to prevent pests and diseases. Submitted image

AMES, Iowa - Spraying pesticides in apple orchards can prove beneficial in the fight against harmful pests and diseases. The question is what is the best method and timing of spraying in order to make the most impact with the least negative consequences on the environment.

Mark Gleason, professor of plant pathology and microbiology, and his team of researchers at Iowa State University have partnered with researchers at The Ohio State University and the USDA-Agricultural Research Service (ARS) to find ways to decrease the amount of chemicals applied to an orchard, while maintaining the orchard’s health. Progress on their three-year research project was recently published in the scientific journal Scientia.

The first spraying system the researchers are studying is an intelligent spraying system, developed by Heping Zhu, USDA-ARS agricultural engineer in Wooster, Ohio, and his team. This system uses a combination of laser beams and sensors mounted on an airblast sprayer to detect where the apple trees’ foliage is located. Based on what the lasers and sensors “see” as the tractor-pulled sprayer passes through the rows of trees, spray nozzles open to specifically target sectors of the foliage. This contrasts with traditional spraying methods, during which all spray nozzles are actively spraying during the entire pass along the tree line, resulting in excess amounts of spray being discharged.

“We’re trying to see how low we can go with spray flow rates while still getting good application coverage and preventing pests and diseases,” Gleason said. “We don’t need trees dripping with pesticide, just enough coverage to do the job.”

So far, the researchers have found this targeted spraying method can reduce the overall pesticide use by 30-70%. Gleason said less pesticide being used benefits the environment and means fewer trips back and forth to refill the sprayer, saving time and fuel.

The other technology they are evaluating is a weather-based disease warning system, which measures how many total hours the humidity level is 90% or higher in an orchard. The warning system starts at the first-cover stage of the season, just after the flower petals fall off. Once the system logs a total of 385 hours under such conditions, fungicide spraying resumes in order to prevent fungal diseases. Using this method, as opposed to pre-scheduling fungicide sprays every 10 to 14 days all season, has been shown to result in an average of 2.3 fewer fungicide spray applications each year – a 25% reduction.

The researchers have been working with six orchards among the two states, including ones near Cambridge and Jefferson, Iowa, as well as at the ISU Horticulture Research Station north of Ames, to conduct research and host on-farm demonstration trials. Monthly meetings take place via Zoom to keep the entire team of researchers, students and orchard owners updated.

The team has also been getting creative in sharing their research progress through a website, blog posts, podcasts and short videos.

One of the videos is a stop motion video created by Olivia Meyer, a graduate student in horticulture and member of Gleason’s research team, that explains how a fungal disease that can impact apples. She breaks down what could be a complex topic into a two-minute, easy to understand clip.

“We’re trying to explain various aspects of our research in fun ways that help communicate to growers what we’re doing,” Meyer said.

This aligns with the research project’s goals, which include educating growers about these more environmentally friendly pesticide application methods. Wendong Zhang, associate professor of economics at Iowa State, and economics graduate student, Nieyan Cheng, are putting together an economic analysis growers can use to determine if either of these systems would offer cost-savings to their operation – another project goal.

“We’re trying to get growers interested in this. A lot of the learning will happen in the hands of the growers,” Gleason said.

The project is being funded by the USDA’s Crop Protection and Pest Management Program.

Yellow card with dark black spots on it representing spray marks. The card is clipped to a tree branch in an apple orchard.
Small slips of water sensitive paper attached to various spots in the tree canopy help researchers measure spray coverage. Keeping track of this can determine the effectiveness of a spraying system. Submitted image